Just use * as the database name.

For problems 712, give a relational algebra expression to find the requested information from the relations defined below. Author(aid : int, name : string, dob : date) Book(bid : int, title : string, aid : int, price : real) Foreign key: aid references Author Customer(cid : int, name : string) Purchase(cid : int, bid : int, when : date) Foreign keys: cid references Customer, bid references Book 7. The cid for customer John Johnson 8. The name of every author who has a name in common with a customer 9. The title of every book purchased since 01-01-2020 10. The first day that a book was purchased 11. The name of every author that has never written a book 12. The name of every customer who has bought all books by Carson Mc- Cullers